1. Field of the Invention
The present invention relates to a method for forming a hollow molding having a thin film on its inner surface, comprising: a primary molding step of injection-molding a pair of semi-hollow bodies by using a stationary mold and a movable mold made movable with respect to the stationary mold, so that its opening may have an abutment portion; a depositing step of forming a thin film on the inner surface of at least one of the semi-hollow bodies formed by the primary molding; and a secondary molding step of integrating the paired semi-hollow bodies to acquire the hollow body, by abutting the opening of the paired semi-hollow bodies deposited, in an upper state where they are left in the molds, and by injecting a molten resin to the abutting portions, a hollow molding obtained by executing the molding method, and a molding apparatus to be used for executing the molding method.
2. Description of the Related Art
A hollow molding having a thin film of several micron orders partially on the inner surface of a hollow body can be exemplified by a front lamp or a tail lamp, which is attached to a vehicle. This lamp is composed of a recessed body portion having an electric bulb, and a lens unit integrally attached to the opening of the body portion. The body portion is molded by an injection molding method, for example, and is suspended in a deposition-dedicated vacuum tank by means of a dedicated hanger while its unnecessary portion such as an outer surface being masked. The body portion is then formed with a thin film by the later-described deposition method. The body portion having the thin film and a lens portion molded separately are set in their individual molds such that the opening of the body portion and the edge of the lens portion are aligned to abut against each other. The body portion and the lens portion are integrated by injecting a molten resin into the abutting joint portion thereby to form a hollow molding having a thin film on its inner surface.
The deposition method for forming a thin film on the inner surface of that body portion or on the surface of a substrate such as the body portion is known in the art. There are known: the sputtering method, in which the thin film is formed by arranging the substrate to be deposited and the target in a confronting manner and by applying and discharging a negative voltage of several kV to the target in an argon gas atmosphere of several Pa to several tens Pa; the vacuum deposition method, in which the film is formed by housing the substrate and the evaporation source in a vacuum container; the ion plating method, in which the vacuum deposition is performed in an argon gas under a pressure of several Pa by applying a negative voltage of several kV to the substrate; and the chemical deposition method.
JP-B-2-38377 discloses a method for forming a hollow molding by an injection molding. Specifically, the hollow molding forming method includes: a primary molding, in which a pair of semi-hollow moldings are so formed by a pair of cavities formed by the stationary mold and the slide mold as to have a joint portion around their opening; and a secondary molding, in which the molds are opened so that one primary semi-hollow molding is left on the stationary mold whereas the other primary semi-hollow molding is left on the slide mode, in which the slide mold is slid to the position where the joint portions of the paired primary semi-hollow molding are registered, in which the molds are then mold clamped, and the joint portions are jointed by injecting the molten resin thereto. Moreover, Japanese Patent No. 3,326,752 discloses such one of the molding method of JP-B-2-38377, that a guide portion is integrally formed at the primary molding time on the inner side of the joint portion or the abutting portion of one primary semi-hollow molding, and that the abutting portion of the other primary semi-hollow molding is guided for the secondary molding, when it is fitted on the abutting portion of one primary semi-hollow molding, by the guide portion of the abutting portion of the one primary semi-hollow molding. On the other hand, Japanese Patent No. 3,047,21 discloses a molding method, in which the hollow molding is formed, as described above, by injecting and filling the resin so that the angle made by the abutting portion from the injecting and filling point at the secondary molding time may be 90 degrees or less.
When the hollow molding having the thin film on its inner surface is to be formed by the method of the related art, there arise many problems because the body portion has to be formed in advance by the injection molding method and has to be transferred into the vacuum tank for the deposition. For example, the body portion is molded in advance and is stored. Therefore, the body portion may be soiled on its surface with sand or dust while being stored, so that it may cause a deposition failure. In order to avoid this, the handling of the body portion requires the highest care and raises the cost. On the other hand, the prefabricated body portion is once stored so that its storage raises a management problem. In addition, the body portion has to be once extracted from the mold before it is deposited, and has to be again mounted in the mold before it is jointed, thus lowering the productivity.
On the other hand, the injection molding method, as disclosed in JP-B-2-38377, is advantageous not only in that the individual steps can be automated to mass-produce the hollow moldings but also in that even the hollow moldings of complicated shapes can be manufactured. According to the invention of Japanese Patent No. 3,326,752, on the other hand, even with more or less deformations, the abutting portions can be brought into fine abutment thereby to raise an effect that the resin for the secondary molding has no leakage. Moreover, the invention of Japanese Patent No. 3,047,213 is characterized in that its joint strength is so high that the molten resin for the secondary molding can be molded even with less injection portions. Because of those advantages and features, the inventions are effectively practiced still at this time. The molding methods of the related art, however, cannot form the thin film of the order of several microns on the inner surface of the hollow molding.